24-01-2020 - Appeal No. 245 of 2019 - Final Order of Judge Rackemann · 51987.2951.01

Working Notes:
M Design and Fourteen Enterprises Pty Ltd as trustee v Noosa Shire Council -
42 Seaview Terrace, Sunshine Beach

Table 5-3 Summary of Shoreline Recession due to Sea Level Rise
 Beach           Profile      Profile        Dune          Depth of          Bruun Rule Recession
 Compartment                  Width         Height          Closure                  (m)
                                (m)        (m AHD)         (m AHD)
                                                                              2050           2100
                                                                           (SLR 0.3m)     (SLR 0.8m)

 Sunshine           ETA          550             17             -12            5.7            15.2
 Beach             602.0


6.4.    Dune Scarp Component
The methodology for calculating the erosion prone area includes an allowance for slumping of the
frontal dune following a short-term erosion event. The Department of Environment and Heritage
Protection (2013) states, “The short-term erosion calculation permits the assessment of shoreline
recession as far as the limit of wave run-up for those cases where the frontal beach ridge is not
overtopped. To allow for slumping of the frontal dune beyond this design run-up level, and the
possible undermining and collapse of structures founded on the dune, a dune scarp component
should be included in the erosion prone area width”.

The angle of repose for dry sand is 35o and this has been used to determine the dune scarp
component of the erosion prone area for the design lifespan of the swimming pool. The short-term
erosion calculations shown in Figure 5-2 and Table 5-2 indicate a dune scarp of approximately 1
metre based on ETA 602.0 and this would result in a dune scarp recession of approximately 1.4
metres.


6.5.    Summary of the Erosion Prone Area Assessment
The erosion prone area reassessment for this appeal has been undertaken in accordance with the
Department of Environment and Heritage Protection (2013) requirements with a planning period of
30 years to accommodate the asset lifespan of the swimming pool. We have also considered the
effect of shoreline recession due to 0.8 metres of sea level rise, short-term erosion associated with a
100 year ARI storm event and dune scarp recession.

Through this assessment there has been careful consideration of the previous assessment
undertaken by BMT WBM (2018). Some components of the erosion prone area have been
calculated by BMT WBM (2018) are considered overly conservative, these include:

       The combination of a 100 year ARI storm tide level and 100 year ARI wave height to define a
        100 year ARI storm event. This is not consistent with the Department of Environment and
        Heritage Protection’s (2013) guidance on this component of the erosion prone area.
       The dune height used for the calculation of recession due to sea level rise was 4.5m which is
        much lower that the actual dune height at Sunshine Beach. This results in an
        underestimation of the volume of sand in the dune system that will accommodate changes
        in the profile position associated with sea level rise.

The erosion prone area calculated for a 30 year planning period is presented in Table 5-4 and Figure
5-4.




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